Stencils and other printing screens more commonly known as silk screens are in a well-established art. These screens are widely used in the visual arts for printing, but they also are used in a field of semi-conductor manufacture. In one such field, stencils are used to print alternating resist layers in producing ceramic hybrid circuits.
This type of printing in the semiconductor manufacturing industry must be carried out at extremely close tolerances. In order to maintain the accuracy and quality of the printing, the stencils must be cleaned regularly. This presents particular problems, since the stencils are difficult to remove from the printing machine. Furthermore, they need adjustment once they are reinstalled in order to ensure that accurate registration with the printed substrate has been re-established. This process of removing, cleaning and reinstalling the stencil is therefore extremely time-consuming.
Another problem of cleaning semiconductor stencils is that volatile and often hazardous chemicals are used for solvents which dissolve and carry off the excess material on the used stencils. This requires extremely specialized cleaning equipment so that the solvent may be introduced to the stencil, and thereafter that the used contaminated solvents be removed from the cleaning area with a minimal amount of air contamination due to solvent evaporation.
Systems for cleaning print screens which are pertinent to the dual use of vacuum and a liquid spray include U.S. Pat. No. 4,808,237 issued to McCormick et al, and U.S. Pat. No. 4,826,539 issued to Charles W. Harpold. These patents represent the closest prior art of which the applicant is aware. The patent to McCormick et al represents a high-pressure hot water system without vacuum assist. The patent to Harpold shows the use of a vacuum in combination with a solvent spray; however, with this device, the screen must first be removed from the printing machine before cleaning. Also, the Harpold air handling and solvent plumbing operate in a manner which is environmentally unsound because the exhaust air is unfiltered and the blower draws a vacuum directly upon the liquid reservoir. Furthermore, the spray pressure is too great to minimize evaporation. Therefore, while pertinent, neither of these references anticipates or suggests the applicant's invention, nor are these devices capable of its results.